The present invention relates to the design and construction of damping systems for suspension systems. More particularly, the present invention relates to the design and construction of a lightweight, low-cost damping cartridge having sealed ends for use in high performance suspension systems, particularly high performance bicycle suspension systems.
Suspension systems incorporating hydraulic damping systems are well-known. Such systems are frequently used in the motorcycle and automotive fields, as well as in the field of bicycles. For example, U.S. Pat. No. 5,456,480 to Turner and McAndrews (the "'480 patent"), which has been assigned to the assignee of the present invention and which is incorporated herein in its entirety, discloses a suspension system for use in a bicycle fork. The suspension system disclosed in the '480 patent includes a damping system in the form of a replaceable damping cartridge unit.
The cartridge unit of the '480 patent has a cylindrical damping cartridge body containing hydraulic oil and enclosing a piston attached to a piston rod. The cartridge unit further includes cartridge seals at both ends. The piston sealingly engages the inner surface of the cartridge body and divides the cartridge body into two chambers. The piston is fixedly mounted to the piston rod so that the piston and piston rod move together along the longitudinal axis of the cartridge body. The piston rod slidably extends through the cartridge seals at both ends of the cartridge body to move the piston along the axial extent of the cartridge body. Ports extend through the piston as well as through the piston rod, so that upon movement of the piston in the cartridge body, hydraulic oil passes from one side of the piston to the other. The restriction of the passages determines the degree of resistance effected as the oil is forced through the passages, and thus determines the amount of damping achieved for a given piston speed.
As illustrated in the '480 patent, the bicycle suspension fork in which the disclosed damping system is used has a pair of telescoping struts, each telescoping strut having an inner tube telescopingly engaged within an outer tube. The damping cartridge is coupled within the inner tube of one of the struts and the piston rod is coupled to the outer tube of that strut. Thus, compression or expansion of the strut causes the damping fluid to move from one side of the piston to the other side and thereby damp the suspension system.
The cartridge seals positioned in the ends of the cartridge body are vital to the proper operation of the cartridge unit, as they prevent oil leakage from between the seal and the inner surface of the cartridge body, and between the seal and the outer surface of the piston rod. Typically, the need to secure the seals properly within the ends of the cartridge body has required that the walls of the cartridge body be sufficiently thick to accommodate threads, a groove for a snap-ring, or to permit an interference-fit connection for retaining a hard rubber seal secured to the inner surface of the end of the cartridge body. In addition, as illustrated in the '480 patent, one end of the cartridge body may further include a flange to seat one of the seals securely therein. The use of such thick walls results in cartridge bodies that have more material than is desirable, and that are, as a result, heavier and more costly to manufacture than desirable. The use of threaded, press-fit, or flange attachments for coupling the cartridge unit to the strut also adds unnecessary weight to, and increases the cost of manufacture of, the cartridge body.
In the '480 patent, a cartridge body has an integral shoulder proximate to its first end that mates with a recess in the upper strut of the telescoping fork assembly. As the shoulder seats against the recess, the cartridge unit is prevented from traveling upward into the upper strut. A snap-ring is then used to prevent the damping cartridge from traveling downward and out of the lower end of the upper strut. Although such a manner of coupling the cartridge body in place within a strut is well constructed and secure, it would be desirable to achieve such coupling in a lighter weight, less costly manner.